Incidence of dentinal defects during root canal preparation with hand files using different irrigants: An in vitro study.

INTRODUCTION: The purpose of this in vitro study was to compare the incidence of dentinal defects during root canal preparation with hand files using different irrigants.
MATERIALS AND METHODS: A total of 120 extracted mandibular incisors were randomly divided into onecontrol group and five experimental groups (n = 20) depending on the irrigant used. Biomechanical preparation was not done in control group. Teeth in experimental groups were prepared with hand K-files to a master apical file #35 with 1-mm increments step-back up to #50. In Group 2, saline was used as an irrigant. In Groups 3, 4, 5, and 6, 3% sodium hypochlorite (NaOCL), SmearClear, 17% ethylenediaminetetraacetic acid (EDTA), and 2% chlorhexidine (CHX), respectively, were used as an irrigant. Specimens were sectioned perpendicular to the long axis at 3, 6, and 9 mm from the apex. Sections were observed under a digital stereomicroscope at 30× magnification. Two-tailed t-test was used for statistical analysis.
RESULTS: There was a statistically significant difference between the six groups. Group 5 (17% EDTA) had the highest number of dentinal defects, followed by Group 3 (3% NaOCl), Group 4 (SmearClear), and Group 6 (2% CHX).
CONCLUSIONS: 17% EDTA causes more dentinal defects as compared to 3% NaOCl, SmearClear, 2% CHX, and saline.

INTRODUCTION

The primary aim of the chemomechanical preparation is to completely remove the microorganisms, pulp tissue, and debris and to enlarge the canal diameter to receive an obturating material.[1] Perforation, canal transportation, ledge or zip formation, and fracture of files are some of the complications that may occur during the root canal preparation.[23] Some recent studies have shown that canal instrumentation also has the potential to cause dentinal defects.[45] These defects can propagate into vertical root fracture if the tooth is subjected to repeated occlusal forces.[67]

The use of irrigants during instrumentation to clean all aspects of the root canal system is central to successful endodontic treatment.[8] Irrigation is complementary to instrumentation in facilitating the removal of pulp tissue and/or microorganisms.[9] A large number of substances have been used as root canal irrigants.

Sodium hypochlorite (NaOCl) with a concentration ranging between 1% and 5.25% is the most widely used irrigant in root canal treatment because of its antimicrobial activity and the capability to dissolve organic tissues.[10]

Chelating agents decalcify the dentin by combining with the calcium ions of the tooth.[11] Ethylenediaminetetraacetic acid (EDTA) is generally accepted as the most effective chelating solution in endodontic therapy. SmearClear (SybronEndo, Orange, CA, USA) is a 17% EDTA solution including cationic and an inorganic surfactant.

2% chlorhexidine (CHX) has been used in endodontics as an irrigating substance due to its biocompatibility,[12] substantivity,[13] lubricating property, and rheological actions.

The purpose of the following in vitro study was to compare the incidence of dentinal defects during root canal preparation with hand files using different irrigants.

MATERIALS AND METHODS

A total of 120 extracted mandibular incisors with single canal were used in this study. Buccolingual and mesiodistal radiographs were taken to verify the presence of the single canal. Teeth with external cracks or defects, deep caries, with previous restorations, immature apices, and teeth with more than one canal were excluded from this study. The root surfaces were observed under ×30 in a digital stereomicroscope to exclude cracks. All the teeth were decoronated using a diamond disc in a micromotor under copious water cooling, leaving a root length of approximately 12 ± 1 mm. A silicon impression material was used for coating the root surface to simulate periodontal ligament (PDL) space. The roots were divided into six groups (n = 20) depending on the irrigant used.

Group 1: Served as a control group, no biomechanical preparation was done

Group 2: Biomechanical preparation was done using saline as an irrigant

Group 3: 3% NaOCl was used as an irrigant

Group 4: SmearClear was used as an irrigant

Group 5: 17% EDTA was used as an irrigant

Group 6: 2% CHX was used as an irrigant.

Shaping and cleaning

The canals were prepared with K-file (Dentsply-Maillefer Ballaigues, Switzerland) to a master apical file #35 with 1-mm increments step-back up to #50. Canals were irrigated with respective irrigant after each instrument change. A volume of 16 ml irrigant was used in each canal.

Sectioning and observation

Specimens were sectioned perpendicular to the long axis at 3, 6, and 9 mm from the apex using Isomet 1000 Precision Saw (Buehler, an ITW Company, IL, USA) under water cooling. Sections were observed under a digital stereomicroscope (Carl Zeiss, Oberkochen, Germany) at ×30 [Figure 1]. Images were blindly checked by two operators for the presence of defects.

Figure 1

Sections observed under a digital stereomicroscope

Definitions of the dentinal defects

Dentinal defects were classified according to Wilcox et al.[6] “No defect” was defined as root dentin devoid of any cracks. “Defect” was defined as fracture lines (Type I defect) and craze lines or partial cracks (Type II defect) [Figure 2].

Figure 2

Classification of dentinal defects: (a) no defect, (b) fracture line (Type I), (c) craze line or partial crack (Type II)

Statistical analysis

Results were expressed as the number and percentage of roots showing dentinal defects in each group. Two-tailed t-test was used for statistical analysis of difference between and among the experimental groups.

RESULTS

No cracks were observed in the control group. Dentinal defects were found in all experimental groups. The results are shown in Table 1 and Graph 1. There was a statistically significant difference between the six groups. Group 5 (17% EDTA) had the highest number of dentinal defects, followed by Group 3 (3% NaOCl), Group 4 (SmearClear), and Group 6 (2% CHX). Groups 3, 4, 5, and 6 were statistically different from Group 1 [Table 2].

Table 1

Number and percentage of root sections presenting different types of dentinal defects in experimental groups

Graph 1

Number of root sections having dentinal defects in all groups

Table 2

Statistical analysis between groups using two-tailed t-test

DISCUSSION

In the present study, mandibular incisors of nearly similar root size were selected to minimize anatomical variations. All teeth were inspected by stereomicroscope and radiograph for the exclusion of teeth with crack or fracture. The sectioning procedure had no influence on crack formation because the control teeth did not show any defects. This is in agreement with other studies that used a similar method.[514] The root surfaces were coated with a layer of silicone impression material before placing within the acrylic blocks to simulate PDLs and distribute stresses during root canal preparation.[15]

In this study, 3% NaOCl, 17% EDTA, SmearClear, and CHX were used because these are the most commonly used endodontic irrigants.

No significant difference was found between Group 1 (control) and Group 2 (saline). This result is consistent with the previous study of Adl et al., which showed fewest cracks with saline.[16]

In the present study, the highest number of dentinal defects was observed in Group 5 (17% EDTA). This means in comparison with other groups, chelating action of 17% EDTA solution induces an adverse softening potential on the calcified components of dentin and reduces the microhardness of dentin.[17]

The present study is in accordance with Saleh and Ettma, who evaluated the effect of NaOCl and EDTA on the microhardness of root canal dentin and reported that both solutions decreased the microhardness of root dentin, but EDTA irrigation induced more reduction.[18]

Group 3 (3% NaOCl) showed significantly more defects when compared to the control group. This finding is compatible with the result of previous studies showing that NaOCl reduces microhardness, elastic modulus, and flexural strength of dentin.[19]

SmearClear (SybronEndo) contains 17% EDTA, cetrimide, and surfactant. Addition of a wetting agent reduces the surface tension and the effectiveness of calcium removal as compared to EDTA.[20]

Significant difference was found between Group 1 (control) and Group 6 (2% CHX). This is in accordance to the study of Oliveira et al., which showed 2% CHX significantly decreased the microhardness of dentin.[21]

Studies have evaluated and compared the potential effects of different preparation systems on dentinal defects; however, a literature search did not reveal any previous studies on the effects of different irrigation solutions on dentinal defect formation during root canal preparation. This study showed that endodontic irrigants are associated with risk of creating dentinal defects.

In our study, few internal craze lines were observed, and most of the defects were external cracks. These results are consistent with the results of a study by Shemesh et al.[4] and Milani et al.[22] This may be due to the stress generated by instrumentation within the canal, which is transmitted to the outer surface of the tooth where it overcomes the bonds holding the dentin together.[23]

CONCLUSIONS

17% EDTA causes more dentinal defects as compared to 3% NaOCl, SmearClear, and 2% CHX.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.